Habitat Fragmentation, Native Insect Pollinators, and Feral Honey Bees in Argentine 'Chaco Serrano'

Abstract

In subtropical dry forest (Chaco Serrano) of Tucuman province, northwestern Argentina, we assessed responses of the flower—visitor assemblage to habitat fragmentation by monitoring insect visits to two spring—flowering tree species and by sampling insects with yellow pan traps. Each of four study sites contained a tract of continuous forest, one large (>2.2 ha) forest fragment, and one small (<1 ha) fragment, with fragments isolated for 5—20 yr preceding the study. During its respective flowering peak each tree species examined, Prosopis nigra (Mimosoideae) and Cercidium australe (Caesalpinoideae), dominated the sites' entomophilous flora. Results indicate that flower—visitor assemblages respond to landscape features on the scale of hectares; specifically, forest fragmentation in the Chaco Serrano leads to an insect flower—visitor fauna increasingly dominated by the exotic honey bee (Apis mellifera). Bees as a group made >90% of observed flower visits to both plant species. The honey bee alone made 82% of all visits to the early—flowering tree species P. nigra and 44% to the later flowering C. australe. Frequency and taxon richness of native flower—visitors at both plant species declined with decreasing forest—fragment size, but frequency of honey bee visits tended to increase in complementary fashion, such that the total frequency of insect visits to flowers of either plant species varied little with fragment size. Frequencies of visits by honey bees and those by native insects were also negatively correlated across individual trees. In both plants, visits by native insects were most consistent (varied the least among plants or over time) in large forest tracts, whereas honey bee visits to C. australe were most consistent in small fragments. In pan trap samples the relative frequency of honey bees increased with decreasing fragment size. Native flower—visitors sampled by pan traps increased in numbers and taxon richness both with increasing patch size and as spring progressed. Thus, fragmentation of the Chaco Serrano appears to (a) affect native flower—visitors adversely and to (b) facilitate honey bees' access to floral resources. It is not clear that these two effects are directly related to each other, however.

Mating patterns and pollinator mobility are critical traits in forest fragmentation genetics

“…Likewise, although many studies show that insect pollination declines in fragmented populations (Aizen and Feinsinger, 1994), there are cases showing long distance pollination by small insects in fragmented landscapes (41 km; Dick et al, 2003;Byrne et al, 2008). Therefore, despite the expectation that selfing and pollen diversity should be a function of pollinator mobility, in line with the landscape ecology models (Charnov, 1976;Karron et al, 2009), more experimental studies into woody plant density, pollen movement and mating patterns are required to further understand these associations.…”

Impact of honeybee (Apis mellifera L.) density on wild bee foraging behaviour

“…floral resources, foraging behaviour, population density, fecundity). An additional causal factor might be because of the various methodologies applied to examine the potential effects of honey bees on wild bees (Aizen & Feinsinger, 1994;Roubik & Wolda, 2001;Thomson, 2004;Forup & Memmott, 2005;Shavit, Amots & Ne'eman, 2009;Gross, 2001). An indicated method to study the competition between honey bees and wild bees is the manipulation of hone-bee abundance by the introduction and/or removal of beehives (Schaffer et al, 1983;Thomson, 2004;Paini, Williams & Roberts, 2005;Shavit, Amots & Ne'eman, 2009).…”

The orchid bee fauna (Hymenoptera, Apidae) of a core area of the Cerrado, Brazil: the role of riparian forests as corridors for forest-associated bees

“…Evidences suggest that habitat alteration may affect local faunas of pollinating insects (e. g. Aizen & Feinsinger 1994, Steffan-Dewenter et al 2002 and that these effects can be more pronounced in tropical areas (Ricketts et al 2008). Evidence of impacts of habitat disturbance on euglossine bees has been found by Nemésio & Silveira (2007a, 2010 and Brosi (2009).…”